The present invention relates to a brass seat union for use in a screw type pipe joint.
Pipe joints of union type construction are used in the portions of the piping arrangement where the disconnection of pipes is necessary, e.g. connections to equipments or machines. In some of the known pipe joints of union type construction, a brass seat member is beforehand attached to the end of the union head in order to eliminate the necessity for the renewal of gaskets and/or additional tightening of the nuts.
FIG. 1 shows a conventional brass seat union joint in which a seat member receiving recess 42 for receiving a seat member 4 is formed in the forward end of a union head 1 as viewed in FIG. 1. The term "forward end" is to be understood here as being the right-side end of the union head 1 opposing the union tail piece 2. The seat member 4 is formed by casting, die casting or cutting from a round bar, to have a comparatively large thickness and an outside diameter which is within the tolerance of shrink fit to the inside diameter of the seat member receiving recess 42. The seat member 4 is then driven into the seat member receiving recess and, thereafter, the surface of the seat member 4 which is to be contacted by the sealing surface 21 of a union tail piece 2 is finished to form a sealing surface. The union head 1 and the union tail piece 2 are provided at their axially outer portions with internal threads for engaging the screw threads on the pipes. The sealing surface 21 is formed on the axially inner end portion of the union tail piece 2 to have an arcuate crosssection in the axial direction and presenting the form of a part of a sphere. A union nut 3 is provided at its inner rear portion with an inward projecting jaw 32 which is adapted to engage with a flange 22 of the union tail piece 2. In use, the union nut 3 is tightly screwed onto the union head 1, through a screwing engagement between the female screw thread 31 in the inner peripheral surface of the front end portion of the union nut 3 and a male screw thread formed on the outer peripheral surface of the axially inner end portion of the union head 1, so that the sealing surface 21 on the union tail piece 2 is strongly pressed against the sealing surface 41 of the union head to provide a tight seal against any leak of the internal fluid. The disconnection can easily be made by unscrewing the union nut 3.
This known brass seat union joint, however, suffers from the following problem. Namely, it is often experienced that the seat member 4 is damaged at its outer peripheral surface when the same is forcibly driven into the seat member receiving portion 42. The use of such a damaged seat member may cause a leak of the internal fluid through the back surface of the seat member 4, i.e. along the surface of the seat member receiving recess 42, and then through the damaged outer peripheral surface of the seat member 4. This leak of fluid, therefore, will be referred to as "back side leak", hereinunder. The leak of the internal fluid may be caused also by a too loose fit between the outer peripheral surface of the seat member 4 and the inner peripheral surface of the seat receiving recess 42. Thus, the union joint of the type described involved a fear of leak of internal fluid, however tight the seal provided by the sealing surfaces 21 and 41 may be. In addition, there is a large fluctuation in the sealing performance because the sealing performance is largely affected by the precision of machining of the sealing surfaces 41 and 21.
FIGS. 2 and 3 designate another example of the known brass sheet union joint. This brass sheet union joint has a union head 1 provided with an annular groove 12 adapted to receive a sheet member 5 having a cylindrical ring-like form as shown in FIG. 5. Then, the inner peripheral wall 13 of the union head 1 is deformed radially outwardly at several portions along the circumference thereof as at portions 15 thereby to fix the seat member 5. In this brass seat union joint, the inner peripheral surface 13 of the union head 1 is deformed only at several portions 15 along its circumference, so that tensile force is applied to other portions 16 of the inner peripheral surface 13, so that the inner peripheral surface 13, which initially has a cylindrical form, tends to be deformed into a polygonal shape having a plurality of substantially curvilinear sides interconnecting adjacent deformed portions 15. Therefore, even though the seat member 5 closely fits in the annular groove 12 in a fluid tight manner, the inner peripheral surface 13 is deflected into the polygonal shape as a result of deformation thereof at the portions 15 to undesirably leave gaps between the wall of the annular groove 12 and the seat member 5, resulting in an external leak of the fluid through such gaps. Furthermore, the portions 15 are often cracked because such portions are deformed by a large force to tightly hold the seat member 5, so that the leak of the fluid is allowed also through such cracks.
Referring again to FIG. 1, the angle .alpha. of taper of the sealing surface 21 on the union head 1 with respect to the axis is usually 90.degree. in the known joint. In some joints for specific uses which is out of the scope of the invention, the angle of taper is smaller than 90.degree..
The inventors have found, through various studies, that a taper angle greater than the conventional value of 90.degree. can provide a higher sealing effect for a given tightening torque applied to the nut 3, provided that the radius of sphere part constituting the sealing surface 21 of the union tail pieces 2 is constant. This fact was proved both experimentally and theoretically for all joints having an equal radius of sphere part constituting the sealing surface 21 on the union tail piece 2.